Thermal Modeling and Sizing of PCB Copper Pads

In low power applications, a surface mounted device (SMD) is naturally cooled by attaching to a printed circuit board (PCB) copper pad. This paper proposes an analytical thermal resistance model and a sizing algorithm for PCB copper pads. Firstly, an axisymmetric thermal resistance model is developed for PCB copper pads where the heat conduction, convection and radiation all exist. Due to the interdependence of the conductive/radiative heat transfer coefficient and the board temperature, a new algorithm is proposed to fast obtain the thermal resistance and to predict the semiconductor junction temperature at different copper pad radii. The algorithm enables a fast sizing of copper pads based on different junction temperature limits. Finally, the developed thermal resistance model and algorithm are verified by computational fluid dynamics (CFD) simulations and experiments.